"By directing policy toward an unlikely scenario of a short-term democratic transition on the island and rejecting most tools of diplomatic engagement, the US is left as a powerless bystander, watching events unfold at a distance," the report says.

It stops short of calling for the trade embargo to be lifted but does urge: an end to restrictions imposed during the Bush administration on travel and remittances to Cuba reinstituting formal co-operation on migration and tackling drug-trafficking allowing Cuba to buy US agricultural products on credit.

"I am prepared to have my administration engage with the Cuban government on a wide range of issues -- from human rights, free speech and democratic reform to drugs, migration and economic issues," he said.

"Let me be clear: I am not interested in talking for the sake of talking. But I do believe that we can move U.S.-Cuban relations in a new direction."

They come a day after Cuban President Raul Castro said he was prepared to discuss "everything, everything, everything" with the United States. Castro told a summit of leftist Latin American leaders gathered in Venezuela, "We are prepared, wherever they want, to discuss everything -- human rights, freedom of the press, political prisoners," Castro said Thursday.

Chavez's press office said Obama walked up to Chavez to greet him, a meeting it called "historic." "President Chavez expressed his hope that relations between the two countries would change," the press office said, quoting Chavez as having told his U.S. counterpart, "Eight years ago with this same hand I greeted Bush. I want to be your friend." It said Obama then thanked Chavez.

Obama's push for a rapprochement with Havana is supported by most Americans, 71 percent of whom said they favor re-establishing diplomatic relations, according to a CNN/Opinion Research Corp. poll carried out April 3-5.

This week, the president opened the door to the discussions by abandoning longstanding restrictions on the ability of Cuban-Americans to travel freely to the island and send money to relatives there.

“I know there is a longer journey that must be traveled in overcoming decades of mistrust, but there are critical steps we can take toward a new day,” Mr. Obama said, adding that he was “prepared to have my administration engage with the Cuban government on a wide range of issues — from human rights, free speech, and democratic reform to drugs, migration, and economic issues.”

He said the United States needed to acknowledge long-held suspicions that it has interfered in the affairs of other countries. But, departing from his prepared text, he also said the region’s countries needed to cease their own historic demonization of the United States for everything from economic crises to drug violence.“That also means we can’t blame the United States for every problem that arises in the hemisphere,” he said. “That’s part of the bargain. That’s the old way, and we need a new way.”

On Cuba, the president’s words were as notable for what he said as for what he did not say. He did not scold or berate the Cuban government for holding political prisoners, as his predecessor, George W. Bush, often did.

But he also did not say that he was willing to support Cuba’s membership in the Organization of American States, or lift the 47-year-old trade embargo against Cuba, as some hemisphere leaders here want him to do.

“Let me be clear,” he said. “I am not interested in talking for the sake of talking. But I do believe we can move U.S.-Cuban relations in a new direction.”

The new tone from Washington drew warm praise from leaders like President Cristina Fernández de Kirchner of Argentina and President Daniel Ortega of Nicaragua. Mr. Ortega, who said he felt ashamed that he was participating in the summit meeting without the presence of Cuba, evoked images of the collapse of the Berlin Wall, saying, “I am convinced that wall will collapse, will come down.”

Mrs. Kirchner praised Mr. Obama for “what you did to stabilize the relationship from the absurd restrictions imposed by the Bush administration,” adding: “We sincerely believe that we in the Americas have a second opportunity to construct a new relationship. Don’t let it slip away.”

Mr. Obama’s speech on Friday night was only the latest in a string of overtures between the countries. On Thursday, Raúl Castro, Cuba’s president, used unusually conciliatory language in describing the Obama administration’s decision to lift restrictions on family travel and remittances.

“We are willing to discuss everything, human rights, freedom of press, political prisoners, everything, everything, everything they want to talk about, but as equals, without the smallest shadow cast on our sovereignty, and without the slightest violation of the Cuban people’s right to self-determination,” Mr. Castro said in Venezuela during a meeting of leftist governments meant as a counterpoint to this weekend’s summit meeting in Trinidad and Tobago.

On Friday, Mrs. Clinton responded, saying, “We welcome his comments, the overture that they represent, and we’re taking a very serious look at how we intend to respond.”

Earlier this week Brazilian officials signaled in Rio de Janeiro that President Luiz Inácio Lula da Silva, potentially flanked by the Colombian president, Álvaro Uribe, would raise the issue of accepting Cuba into the Organization of American States at the summit meeting. Cuba’s “absence is an anomaly and he is waiting for this situation to be corrected,” Marco Aurélio García, Mr. da Silva’s foreign policy adviser, told reporters.

On Friday, the secretary general of the O.A.S., José Miguel Insulza, said he would call for Cuba to be readmitted. And Mr. Chávez recently said he would refuse to sign the official declaration produced at the summit meeting because Cuba was not invited.

Even for those who believed that brutal treatment could produce results, the official said, “seeing these depths of human misery and degradation has a traumatic effect.”

A footnote to another of the memos described a rift between line officers questioning Abu Zubaydah at a secret C.I.A. prison in Thailand and their bosses at headquarters, and asserted that the brutal treatment may have been “unnecessary.”

In March 2002, when Abu Zubaydah was captured in Pakistan after a gunfight with Pakistani security officers backed by F.B.I. and C.I.A. officers, Bush administration officials portrayed him as a Qaeda leader. That judgment was reflected in the Aug. 1, 2002, legal opinion signed by Jay S. Bybee, then head of the Justice Department’s Office of Legal Counsel.The memo summarizes the C.I.A.’s judgment that Abu Zubaydah, then 31, had risen rapidly to “third or fourth man in Al Qaeda” and had served as “senior lieutenant” to Osama bin Laden. It said he had “managed a network of training camps” and had been “involved in every major terrorist operation carried out by Al Qaeda.”

The memo reported the C.I.A.’s portrayal of “a highly self-directed individual who prizes his independence,” a deceptive narcissist, healthy and tough, who agency officers believed was the most senior terrorist caught since the attacks of Sept. 11, 2001.

His interrogation, according to multiple accounts, began in Pakistan and continued at the secret C.I.A. site in Thailand, with a traditional, rapport-building approach led by two F.B.I. agents, who even helped care for him as his gunshot wounds healed.

A C.I.A. interrogation team that arrived a week or two later, which included former military psychologists, did not change the approach to questioning, but began to keep him awake night and day with blasting rock music, have his clothes removed and keep his cell cold.

The legal basis for this treatment is uncertain, but lawyers at C.I.A. headquarters were in constant touch with interrogators, as well as with Mr. Bybee’s subordinate in the Office of Legal Counsel, John C. Yoo, who was drafting memos on the legal limits of interrogation.

Through the summer of 2002, Abu Zubaydah continued to provide valuable information. Interrogators began to surmise that he was not a leader, but rather a helpful training camp personnel clerk who would arrange false documents and travel for jihadists, including Qaeda members.

He knew enough to give interrogators “a road map of Al Qaeda operatives,” an agency officer said. He also repeated talk he had heard about possible plots or targets in the United States, though when F.B.I. agents followed up, most of it turned out to be idle discussion or preliminary brainstorming.At the time, former C.I.A. officials say, his tips were extremely useful, helping to track several other important terrorists, including Mr. Mohammed.

But senior agency officials, still persuaded, as they had told President George W. Bush and his staff, that he was an important Qaeda leader, insisted that he must know more.“You get a ton of information, but headquarters says, ‘There must be more,’ ” recalled one intelligence officer who was involved in the case. As described in the footnote to the memo, the use of repeated waterboarding against Abu Zubaydah was ordered “at the direction of C.I.A. headquarters,” and officials were dispatched from headquarters “to watch the last waterboard session.”

The memo, written in 2005 and signed by Steven G. Bradbury, who worked in the Office of Legal Counsel, concluded that the waterboarding was justified even if the prisoner turned out not to know as much as officials had thought.

And he did not, according to the former intelligence officer involved in the Abu Zubaydah case. “He pleaded for his life,” the official said. “But he gave up no new information. He had no more information to give.”

Since 2002, the C.I.A. has downgraded its assessment of Abu Zubaydah’s significance, while continuing to call his revelations important. In an interview, an intelligence officer said that the current view was that Abu Zubaydah was “an important terrorist facilitator” who disclosed “essential raw material for successful counterterrorist action.”

The role played by psychologists in adapting SERE methods for interrogation has been described in books and news articles, including some in The Washington Post. Author Jane Mayer and journalist Katherine Eban separately identified as key figures James Mitchell and Bruce Jessen, two psychologists in Washington state who worked as CIA contractors after 2001 and had extensive experience in SERE training.

The CIA psychologists had personal experience with SERE and helped convince CIA officials that harsh tactics would coerce confessions from Abu Zubaida without inflicting permanent harm. Waterboarding was touted as particularly useful because it was "reported to be almost 100 percent effective in producing cooperation," the memo said.

The agency then used a psychological assessment of Abu Zubaida to find his vulnerable points. One of them, it turns out, was a severe aversion to bugs. "He appears to have a fear of insects," states the memo, which describes a plan to place a caterpillar or similar creature inside a tiny wooden crate in which Abu Zubaida was confined. CIA officials say the plan was never carried out.

Former intelligence officials contend that Abu Zubaida was found to have played a less important role in al-Qaeda than initially believed and that under harsh interrogation he provided little useful information about the organization's plans.

The role of health professionals as described in the documents has prompted a renewed outcry from ethicists who say the conduct of psychologists and supervising physicians violated basic standards of their professions.

the documents show a steady stream of psychologists, physicians and other health officials who both kept detainees alive and actively participated in designing the interrogation program and monitoring its implementation. Their presence also enabled the government to argue that the interrogations did not include torture.

"The health professionals involved in the CIA program broke the law and shame the bedrock ethical traditions of medicine and psychology," said Frank Donaghue, chief executive of Physicians for Human Rights, an international advocacy group made up of physicians opposed to torture. "All psychologists and physicians found to be involved in the torture of detainees must lose their license and never be allowed to practice again."

The alleged actions of medical professionals in the secret prisons are viewed as particularly troubling by an array of groups, including the American Medical Association and the International Committee of the Red Cross. AMA policies state that physicians "must not be present when torture is used or threatened." The guidelines allow doctors to treat detainees only "if doing so is in their [detainees'] best interest" and not merely to monitor their health "so that torture can begin or continue."

"The release of CIA memos on interrogation methods by the US department of justice appears to have offered a get-out-of-jail-free card to people involved in torture," Amnesty International said. "Torture is never acceptable and those who conduct it should not escape justice."

The Bush administration lawyers argued in the memos that the techniques did not amount to torture because no serious psychological or physical harm was done. About 10 techniques, with variations, were approved, ranging from waterboarding, which simulates drowning, to sleep deprivation and playing on a detainee's perceived fear of insects.

Hayden and Mukasey, in a jointly written piece in the Wall Street Journal today, declared there was no need to release the memos. "Disclosure of the techniques is likely to be met by faux outrage and is perfectly packaged for media consumption. It will also incur the utter contempt of our enemies."Somehow, it seems unlikely that the people who beheaded Nicholas Berg [the US businessman who was killed in Iraq] and Daniel Pearl [the US journalist killed in Pakistan], and have tortured and slain other American captives, are likely to be shamed into giving up violence by the news that the US will no longer interrupt that sleep cycle of captured terrorists even to help elicit intelligence that could save the lives of its citizens."

One of the memos, dated 2005, said that the CIA had 94 detainees in its custody at the time and had used the approved techniques against 28 of them, and that these amounted to the hard core of prisonersThree of the memos were written by Steven Bradbury, of the US justice department, in response to questions from John Rizzo, a lawyer with the CIA, who wanted to know if the techniques complied with international laws.

Stacy Sullivan, of Human Rights Watch, echoed this: "President Obama said there was nothing to gain 'by laying blame for the past'. But prosecuting those responsible for torture is really about ensuring that such crimes don't happen in the future."

The Geneva-based International Commission of Jurists issued a statement calling on Obama to investigate and prosecute officials who authorised and engaged in torture."Without holding to account the authors of a policy of torture and those executing it, there cannot be a return to the rule of law," said Wilder Tayler, acting secretary-general of the ICJ.

Cramped confinement: Detainees put in uncomfortably small containers. But this was judged to be unsuccessful, as it offered detainees a temporary save haven.

Speaking to leaders gathered in Port of Spain, Mr Obama declared: "The US seeks a new beginning with Cuba."

"I know there is a longer journey that must be travelled to overcome decades of mistrust, but there are critical steps we can take toward a new day," he said.

Cuba is excluded from the summit, which includes 34 members of the Organisation of American States (OAS), though Latin American leaders have been calling for the communist country to be readmitted.

speaking on Friday in the Dominican Republic, Mrs Clinton acknowledged that US policy towards Cuba had "failed" and said Washington was "taking a very serious look at how to respond."

Addressing the summit, Mr Obama said he wanted to move forward with a sense of "equal partnership" with all the nations of the Americas despite decades of mistrust.

Mr Obama earlier greeted and shook hands with Venezuela's President, Hugo Chavez, during an impromptu meeting. Photographs released by the Venezuelan government showed Mr Chavez - one of the Bush's administrations most strident critics - smiling and clasping hands with Mr Obama at the start of the summit.

Before the summit began Mr Chavez appeared to chastise the US for its approach to Cuba, which is not a member of the OAS. In a pre-summit statement, he also said that "there is more democracy in Cuba than in the United States". But he greeted the US president warmly when the opportunity arrived, gripping the Mr Obama's hand in welcome. "I greeted Bush with this hand eight years ago; I want to be your friend," Mr Chavez told Mr Obama, according to a Venezuelan presidential press office statement.

now he has started a review of policy toward Afghanistan and Pakistan intended to find a new strategy, and he signaled that reconciliation could emerge as an important initiative, mirroring the strategy used by Gen. David H. Petraeus in Iraq.

“If you talk to General Petraeus, I think he would argue that part of the success in Iraq involved reaching out to people that we would consider to be Islamic fundamentalists, but who were willing to work with us because they had been completely alienated by the tactics of Al Qaeda in Iraq,” Mr. Obama said. At the same time, he acknowledged that outreach may not yield the same success. “The situation in Afghanistan is, if anything, more complex,” he said. “You have a less governed region, a history of fierce independence among tribes. Those tribes are multiple and sometimes operate at cross purposes, and so figuring all that out is going to be much more of a challenge.”

administration officials have criticized the Pakistani government for its own reconciliation deal with local Taliban leaders in the Swat Valley, where Islamic law has been imposed and radical figures hold sway. Pakistani officials have sought to reassure administration officials that their deal was not a surrender to the Taliban, but rather an attempt to drive a wedge between hard-core Taliban leaders and local Islamists.

During the interview, Mr. Obama also left open the option for American operatives to capture terrorism suspects abroad even without the cooperation of a country where they were found. “There could be situations — and I emphasize ‘could be’ because we haven’t made a determination yet — where, let’s say that we have a well-known Al Qaeda operative that doesn’t surface very often, appears in a third country with whom we don’t have an extradition relationship or would not be willing to prosecute, but we think is a very dangerous person,” he said.“I think we still have to think about how do we deal with that kind of scenario,”

The president went on to say that “we don’t torture” and that “we ultimately provide anybody that we’re detaining an opportunity through habeas corpus to answer to charges.”Aides later said Mr. Obama did not mean to suggest that everybody held by American forces would be granted habeas corpus or the right to challenge their detention. In a court filing last month, the Obama administration agreed with the Bush administration position that 600 prisoners in a cavernous prison on the American air base at Bagram in Afghanistan have no right to seek their release in court.

The report cited two alleged incidents from January 3. In one, it said, after a tank round struck near a house, a father and his two sons -- both younger than 11 -- emerged to look at the damage. "As they exited their home, IDF soldiers shot and killed them (at the entrance to their house), with the daughter witnessing," the report said. In the second, it said, "Israeli soldiers entered a family house in the Zeitoun neighborhood of Gaza City. Standing at the doorstep, they asked the male head of the household to come out and shot him dead, without warning, while he was holding his ID, hands raised up in the air, and then started to fire indiscriminately and without warning into the room where the rest of the family was huddled together. "The eldest son was shouting in vain the word 'Children' in Hebrew to warn the soldiers. The shooting did not stop until everyone was lying on the floor. The mother and four of the brothers, aged 2-12 years, had been wounded, one of them, aged 4, fatally."

The alleged instances occurred during Operation Cast Lead, which was launched December 27 to halt rocket attacks into southern Israel from Gaza and ended January 17 with a cease-fire. The U.N. report called the response by Israel disproportionate. Of the 1,453 people estimated killed in the conflict, 1,440 were Palestinian, including 431 children and 114 women, the report said. The 13 Israelis killed included three civilians and six soldiers killed by Hamas, and four soldiers killed by friendly fire, it said.

The report said the Israeli operation resulted in "a dramatic deterioration of the living conditions of the civilian population." It cited "targeted and indiscriminate" attacks on hospitals and clinics, water and sewage treatment facilities, government buildings, utilities and farming and said the offensive "intensified the already catastrophic humanitarian situation of the Palestinian people." It said Israeli strikes damaged more than 200 schools and left more than 70,000 people homeless. "There are strong and credible reports of war crimes and other violations of international norms," it said, adding that many observers have said war crimes investigations should be undertaken.

Mark Regev, a spokesman for Israeli Prime Minister Ehud Olmert, called the report "another example of the one-sided and unfair attitude of the rapporteur of the Human Rights Council, a council that has been criticized by current and previous secretaries-general for its unbalanced attitudes toward Israel." He added, "The negative fixation on Israel by the council has done a disservice to the issue of human rights internationally as has been attested to by the leading NGO's [nongovernmental organizations] on human rights."

Another report issued Monday also was critical of the IDF. The report from Physicians for Human Rights said the Gaza incursion violated IDF's own code of ethics. The report by the medical group, which shared the 1997 Nobel Peace Prize, cited instances where it said IDF forces did not evacuate injured civilians for days and prevented Palestinian teams from reaching the wounded, and said some of them died as a result. It said 16 Palestinian medical personnel were killed by IDF fire and 25 were wounded during the IDF operation, and accused the IDF of attacking 34 medical centers in violation of the IDF's own "ethical code for fighting terror." In response, the IDF accused Hamas of having used medical vehicles, facilities and uniforms to conceal its members' activity. "Hamas used ambulances to 'rescue' terror activists from the battlefield and used hospitals and medical facilities as hiding places," the Israelis said in a written statement. "Despite this, throughout the fighting, IDF forces were instructed to avoid firing at ambulances, even if they were being used by armed fighters. They were instructed only to shoot if there was fire towards our forces emanating from the direction of the ambulance." Regarding the reported delays in casualty evacuations, "there existed real difficulties in evacuating the injured, due to the roadblocks, booby-trapped roads and dirt mounds placed by the Hamas as well as the considerable damage to the infrastructure," the statement said.

he Israeli daily Haaretz newspaper reported that Israeli soldiers who had finished basic training ordered the shirts, one of which showed a pregnant Arab in the crosshairs of a gun sight with a caption reading "1 Shot 2 Kills." Another showing a small child in a gun's sight was captioned, "The smaller they are, the harder it is." "The examples presented by The Haaretz reporter are not in accordance with IDF values and are simply tasteless," the Israeli military said in a written statement. "This type of humor is unbecoming and should be condemned."

Israeli soldiers said last week that Palestinian civilians were killed and Palestinian property intentionally destroyed during Israel's military campaign in Gaza, according to Haaretz. The IDF has said it is investigating the claims, but its top general expressed skepticism Monday. "I don't believe that soldiers serving in the IDF hurt civilians in cold blood, but we shall wait for the results of the investigation," Lt. Gen. Ashkenazi, the chief of staff, said in a speech. "I tell you that this is a moral and ideological army." He blamed Hamas for choosing "to fight in heavily populated areas. "It (was) a complex atmosphere that includes civilians and we took every measure possible to reduce harm of the innocent," he said, according to an IDF statement.

On Monday, Israel's chief of staff defended his troops against a rising tide of criticism. "I tell you that this is a moral and ideological army," Lt-Gen Gabi Ashkenazi said in a speech to new recruits. "I have no doubt that exceptional events will be dealt with. We took every measure possible to reduce harm to the innocent [in Gaza]."

But he said he was optimistic, due to President Obama's "different" approach.

Mr Qureshi also appealed for better equipment and training for Pakistan's armed forces.

Often using the detainee's own words, the report offers a harrowing view of conditions at the secret prisons, where prisoners were told they were being taken "to the verge of death and back," according to one excerpt. During interrogations, the captives were routinely beaten, doused with cold water and slammed head-first into walls. Between sessions, they were stripped of clothing, bombarded with loud music, exposed to cold temperatures, and deprived of sleep and solid food for days on end. Some detainees described being forced to stand for days, with their arms shackled above them, wearing only diapers. "On a daily basis . . . a collar was looped around my neck and then used to slam me against the walls of the interrogation room," the report quotes detainee Tawfiq bin Attash, also known as Walid Muhammad bin Attash, as saying. Later, he said, he was wrapped in a plastic sheet while cold water was "poured onto my body with buckets." He added: "I would be wrapped inside the sheet with cold water for several minutes. Then I would be taken for interrogation."

President George W. Bush acknowledged the use of coercive interrogation tactics on senior al-Qaeda captives detained by the CIA in the aftermath of the Sept. 11, 2001, terrorist attacks, but he insisted that the measures complied with U.S. and international law. Former CIA director Michael V. Hayden confirmed last year that the measures included the use of waterboarding on three captives before 2003. President Obama outlawed such practices within hours of his inauguration in January. But Obama has expressed reluctance to conduct a legal inquiry into the CIA's policies.

Abu Zubaida was severely wounded during a shootout in March 2002 at a safe house he ran in Faisalabad, Pakistan, and survived thanks to CIA-arranged medical care, including multiple surgeries. After he recovered, Abu Zubaida describes being shackled to a chair at the feet and hands for two to three weeks in a cold room with "loud, shouting type music" blaring constantly, according to the ICRC report. He said that he was questioned two to three hours a day and that water was sprayed in his face if he fell asleep. At some point -- the timing is unclear from the New York Review of Books report -- Abu Zubaida's treatment became harsher. In July 2002, administration lawyers approved more aggressive techniques. Abu Zubaida said interrogators wrapped a towel around his neck and slammed him into a plywood wall mounted in his cell. He was also repeatedly slapped in the face, he said. After the beatings, he was placed in coffinlike wooden boxes in which he was forced to crouch, with no light and a restricted air supply, he said. "The stress on my legs held in this position meant my wounds both in my leg and stomach became very painful," he told the ICRC. After he was removed from a small box, he said, he was strapped to what looked like a hospital bed and waterboarded. "A black cloth was then placed over my face and the interrogators used a mineral bottle to pour water on the cloth so that I could not breathe," Abu Zubaida said. After breaks to allow him to recover, the waterboarding continued.

By Tuesday night, the seat of government had been badly battered and scores of people had been injured. But riot police had regained control of the president’s offices and Parliament Wednesday.

Young people have increasingly used the Internet to mobilize politically; cellphones and text messages helped swell protests in Ukraine in 2004, and in Belarus in 2006.

The immediate cause of the protests were parliamentary elections held on Sunday, in which Communists won 50 percent of the vote, enough to allow them to select a new president and amend the Constitution. Though the Communists were expected to win, their showing was stronger than expected, and opposition leaders accused the government of vote-rigging.

Election observers from the European Union and the Organization for Security and Cooperation in Europe had tentatively accepted the voting as fair, though they expressed some concern about interference from the authorities. But the results were a deep disappointment in the capital, where Communist candidates lost the last round of municipal elections.

Behind the confrontation is a split in Moldova’s population. The collapse of the Soviet Union brought benefits to much of Eastern Europe, but in Moldova it ushered in economic decline and instability. In 2001, angry citizens backed the return of the Communists and their social programs.

But Moldova remained desperately poor, and young people flocked overseas to work. They have looked to the West as the best path to economic stability and have defied Mr. Voronin’s government by urging closer integration with Romania.

“I wouldn’t necessarily call it an anti-Communist movement,” Mr. Patterson said. “This really is a generational squeeze. It’s not really the Communists versus the opposition. It’s the grandmothers versus the grandkids.”

In late January, Mr. Rajoelina began a string of protests that sometimes led to lootings and confrontations with security forces. More than 100 people have died during the recent political violence, including at least 28 shot by security forces on Feb. 7. During a time when Mr. Ravalomanana seemed to have the upper hand, he fired the younger man as mayor. While Mr. Rajoelina enjoys considerable popularity, he also is widely disliked. He does not come to power at the crest of a wave of support but as the result of an opportunity created by a divided military.

Some senior Obama administration officials, including Attorney General Eric H. Holder Jr., have labeled one of the 14 approved techniques, waterboarding, illegal torture.

The United States prosecuted some Japanese interrogators at war crimes trials after World War II for waterboarding and other methods detailed in the memos.

Together, the four memos give an extraordinarily detailed account of the C.I.A.’s methods and the Justice Department’s long struggle, in the face of graphic descriptions of brutal tactics, to square them with international and domestic law. Passages describing forced nudity, the slamming of detainees into walls, prolonged sleep deprivation and the dousing of detainees with water as cold as 41 degrees alternate with elaborate legal arguments concerning the international Convention Against Torture.

The documents were released with minimal redactions, indicating that President Obama sided against current and former C.I.A. officials who for weeks had pressed the White House to withhold details about specific interrogation techniques.

Leon E. Panetta, the C.I.A. director, had argued that revealing such information set a dangerous precedent for future disclosures of intelligence sources and methods.

A more pressing concern for the C.I.A. is that the revelations may give new momentum to proposals for a full-blown investigation into Bush administration counterterrorism programs and possible torture prosecutions.

Mr. Obama condemned what he called a “dark and painful chapter in our history” and said that the interrogation techniques would never be used again. But he also repeated his opposition to a lengthy inquiry into the program, saying that “nothing will be gained by spending our time and energy laying blame for the past.”

Mr. Obama said that C.I.A. officers who were acting on the Justice Department’s legal advice would not be prosecuted, but he left open the possibility that anyone who acted without legal authorization could still face criminal penalties. He did not address whether lawyers who authorized the use of the interrogation techniques should face some kind of penalty.

The four legal opinions, released in a Freedom of Information Act lawsuit filed by the A.C.L.U., were written in 2002 and 2005 by the Justice Department’s Office of Legal Counsel, the highest authority in interpreting the law in the executive branch.

The first of the memos, from August 2002, was signed by Jay S. Bybee, who oversaw the Office of Legal Counsel, and gave the C.I.A. its first detailed legal approval for waterboarding and other harsh treatment.

Three others, signed by Steven G. Bradbury, sought to reassure the agency in May 2005 that its methods were still legal, even when multiple methods were used in combination, and despite the prohibition in international law against “cruel, inhuman or degrading” treatment.

All legal opinions on interrogation were revoked by Mr. Obama on his second day in office, when he also outlawed harsh interrogations and ordered the C.I.A.’s secret prisons closed.

They recounted the C.I.A.’s assertions of the effectiveness of the techniques but noted that interrogators could not always tell a prisoner who was withholding information from one who had no more information to offer.

The memos include what in effect are lengthy excerpts from the agency’s interrogation manual, laying out with precision how each method was to be used. Waterboarding, for example, involved strapping a prisoner to a gurney inclined at an angle of “10 to 15 degrees” and pouring water over a cloth covering his nose and mouth “from a height of approximately 6 to 18 inches” for no more than 40 seconds at a time.

But a footnote to a 2005 memo made it clear that the rules were not always followed. Waterboarding was used “with far greater frequency than initially indicated” and with “large volumes of water” rather than the small quantities in the rules, one memo says, citing a 2004 report by the C.I.A.’s inspector general.

Most of the methods have been previously described in news accounts and in a 2006 report of the International Committee of the Red Cross, which interviewed 14 detainees. But one previously unknown tactic the C.I.A. proposed — but never used — against Abu Zubaydah, a terrorist operative, involved exploiting what was thought to be his fear of insects.

“As we understand it, you plan to inform Zubaydah that you are going to place a stinging insect into the box, but you will actually place a harmless insect in the box, such as a caterpillar,” one memo says.

Dennis C. Blair, the director of national intelligence, cautioned that the memos were written at a time when C.I.A. officers were frantically working to prevent a repeat of the Sept. 11, 2001, attacks. “Those methods, read on a bright, sunny, safe day in April 2009, appear graphic and disturbing,” said Mr. Blair in a written statement. “But we will absolutely defend those who relied on these memos.”

Ten techniques are approved, listed as: attention grasp, walling (in which the suspect could be pushed into a wall), a facial hold, a facial slap, cramped confinement, wall standing, sleep deprivation, insects placed in a confinement box (the suspect had a fear of insects) and the waterboard. In the latter, "the individual is bound securely to an inclined bench, which is approximately four feet by seven feet. The individual's feet are generally elevated. A cloth is placed over the forehead and eyes. Water is then applied to the cloth in a controlled manner........produces the perception of 'suffocation and incipient panic'."

'Walling' involved use of a plastic neck collar to slam suspects into a specially-built wall that the CIA said made the impact sound worse than it actually was. Other methods include food deprivation.

The techniques were applied to at least 14 suspects.

In the first of the memos, dated 1 August 2002, the justice department gave the go-ahead to John Rizzo, then acting general counsel to the CIA, for operatives to move to the "increased pressure phase" in interrogating an al-Qaida suspect.

civil rights organisations have been disappointed by a series of rulings by the Obama administration that have protected a lot of material relating to Guantánamo and the sites abroad. The release of the memos today reversed that trend, though there will be unhappiness over the immunity from prosecution.

Echoing the president, the attorney-general, Eric Holder, reiterated that there would be no prosecution of CIA operatives working within the guidelines set by the Bush administration."It would be unfair to prosecute dedicated men and women working to protect America for conduct that was sanctioned in advance by the justice department," Holder said.

The director of the CIA, Leon Panetta, told CIA employees that "this is not the end of the road on these issues", apparently in expectation of Congressional inquiries and court actions abroad. He promised legal and financial help for any CIA employees who faced such action.

In Spain, the chances of court action against six senior Bush administration members over the torture receded today after a ruling by the attorney-general, Candido Conde-Pumpido.He said that any such action should be heard in a US court rather than a Spanish one, and that he would not allow Spain's legal system to be used as a plaything for political ends.

Spanish human rights lawyers last month asked Judge Baltasar Garzón, who indicted the former Chilean president Augusto Pinochet in 1998, to consider filing charges against the former US attorney-general, Alberto Gonzales, and five others.

Obama, in a statement from the White House, said: "In releasing these memos, it is our intention to assure those who carrying out their duties relying in good faith upon the legal advice from the department of justice that they will not be subject to prosecution."

Sudan expelled 13 foreign aid groups in March after the ICC issued an arrest warrant against Sudanese President Omar al-Bashir.

Mr Bashir is accused of orchestrating atrocities against civilians in Darfur, where his government has been fighting rebels since 2003. The UN says that up to 300,000 people have died during the conflict and 2.7 million driven from their homes.